Electronic Structure Methods for Small-Gap Systems

加州大学欧文分校的Filipp Furche得到了化学理论，模型和计算方法计划（化学部），凝聚态物质和材料理论计划（材料研究部）以及计算和数据支持科学与工程计划（CDS& E）的支持，以开发，实施，测试，并应用计算方法，为一类重要的分子系统提供预测准确性，这些分子系统很难通过实验或当前的计算方法来表征。这些系统被称为小带隙系统，在最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）之间具有小的能隙。 含有过渡金属如铁或铂或甚至更重的镧系元素和锕系元素的分子和离子可以属于这一类。 催化剂的合理设计关键取决于我们对这些分子进行建模的能力。 然而，精确的模拟具有几个以上原子的小间隙系统一直是非常难以捉摸的。 Furche和他的研究小组开发的方法和计算机程序能够模拟化学结构，过程和具有基础和技术重要性的材料。该项目开发的方法通过Turbomole量子化学软件向公众提供。该项目还涉及加州大学欧文分校的本科课程开发和针对弱势社区高中生的外展计划。 Furche群以前的工作已经建立了无规相位近似（RPA）-重整化多体微扰理论能够系统地改进小能隙系统的半局域DFT结果。拟议的项目以这些结果为基础，旨在通过开发一系列强大且广泛适用的计算工具来改变计算和实验化学家和材料科学家处理小间隙分子的方式。提出了一种与频率相关的RPA重整化Bethe-Salpeter核来提高RPA类方法的精度。电子激发态和频率相关响应特性通过时间相关响应理论来访问。化学发展的目标是进一步降低RPA和超越RPA计算的成本，并将其范围扩展到具有数百个原子的系统。

Filipp Furche of the University of California, Irvine is supported by an award from the Chemical Theory, Models and Computational Methods Program (Division of Chemistry), the Condensed Matter and Materials Theory Program (Division of Materials Research) and the Computational and Data-Enabled Science and Engineering Program (CDS&E) to develop, implement, test, and apply computational methods that deliver predictive accuracy for an important class of molecular systems that are very difficult to characterize either by experiment or by current computational approaches. These systems, known as small band-gap systems, have a small energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Molecules and ions containing transition metals such as iron or platinum or the even heavier lanthanides and actinides can fall into this category. The rational design of catalysts crucially relies on our ability to model such molecules. However, accurate simulations of small-gap systems with more than a few atoms have been very elusive. The methods and computer programs developed by Furche and his research group enable simulations of chemical structures, processes, and materials of fundamental and technological importance. The methods developed in this project are made available to the public through the Turbomole quantum chemistry software. This project also involves undergraduate curriculum development at UC Irvine and an outreach program for high school students in disadvantaged neighborhoods. Previous work in the Furche group has established that random phase approximation (RPA)-Renormalized many-body perturbation theory is capable of systematically improving semi-local DFT results for small-gap systems. The proposed project builds on these results and aims to transform the way computational and experimental chemists and materials scientists approach small-gap molecules by developing an armamentarium of robust and widely applicable computational tools. A frequency-dependent RPA renormalized Bethe-Salpeter kernel is proposed to boost the accuracy of RPA-type methods. Electronically excited states and frequency-dependent response properties are accessed via time-dependent response theory. Algorithmic developments aim to further reduce the cost of RPA and beyond-RPA calculations and extend their scope to systems with hundreds of atoms.